The present invention relates to an improved scroll fluid machine such as a scroll vacuum pump of the overall rotation type.
FIG. 1 shows a longitudinally sectional view of a conventional scroll fluid machine disclosed in the Japanese Patent Application (OPI) No. 46081/80 (the term "OPI" as used herein means an "unexamined published application") and comprising a casing 1, an electric motor 2, a rib 3, a bearing holder 4, a fixed scroll 5, a rotary scroll 6, a gas intake port 7, a gas discharge port 8, and oil return holes 9. The casing 1 contains lubricating oil 10 at the bottom of the casing. The motor 2 is provided in the casing 1 and has a rotary shaft 2a having an oil passage 2b extending through the shaft in the axial direction thereof and open in the lubricating oil 10. The rib 3 is coupled to the inside surface of the casing 1. The bearing holder 4 is coupled to the rib 3 and supports the rotary shaft 2a rotatably. The fixed scroll 5 is coupled to the bearing holder 4. The rotary scroll 6 is eccentrically rotated by the rotary shaft 2a relative to the fixed scroll 5. The gas intake port 7 communicates with the internal opening of the fixed scroll 5. A gas compressed by the fixed and the rotary scrolls 5 and 6 is discharged from the casing 1 through the gas discharge port 8. The oil return holes 9 vertically extend through the rib 3 to return the lubricating oil down from over the bearing holder 4. When the electric motor 2 is rotated, the rotary scroll 6 is revolved so that the gas is introduced into the casing 1 through the gas intake port 7, compressed by both the scrolls 5 and 6 and discharged form the casing 1 through the gas outlet port 8. At that time, the lubricating oil 10 stored in the casing 1 at the bottom thereof is supplied to the scrolls 5 and 6 through the oil passage 2b due to a pressure difference in the casing, lubricates the sliding portions of the scroll fluid machine, and is returned to the bottom of the casing through the oil return holes 9. The machine can thus be used as a vacuum pump. However, since the oil passage 2b is provided in the rotary shaft 2 to use the lubricating oil 10 to lubricate a bearing, a coupling and so forth and prevent the gas from leaking through a small clearance, the constitution of the scroll fluid machine is complicated. This is a problem. Besides, dust or chips generated as a result of the wear of the machine and deposited on the bottom of he inside of the body of the machine is agitated together with the lubricating oil 10 so as to be moved to the sliding portions of the machine to promote the wear thereof. This is another problem.7